In the past, fax machines were generally interconnected using conventional analog telephone circuits operating using a time division multiplex protocol (hereinafter called TDM). However, currently, many fax messages are transmitted over packet networks. When fax machines are interconnected over a packet network, the initial connection is typically made using a voice grade connection. Subsequently, when the actual fax transmission begins, the network connection generally switches to a protocol known as fax relay.
Fax machines known as Group 3 fax machines are capable of operating at top speed of 14,400 bits per second (hereinafter bps). More modern fax machines, known as Super Group 3 fax machines are capable of operating at speeds of up to 33,600 bps. In general, Group 3 fax machines utilize a protocol known as the V.21 fax protocol and Super Group 3 fax machines utilize a protocol known as the V.34 half duplex protocol. The V.21 and V.34 protocols are standard protocols that have been documented and published by International Telecommunication Union standard committees.
When fax machines are connected over a TDM circuit, the calling machine initially tries to connect at the highest speed at which the fax machine is capable of operating. If a connection can not be made at that speed, the machine typically “falls back” and tries to make a connection at a slower speed. For example, when a V.34 Super Group 3 fax machine connects to a Group 3 fax machine over a TDM circuit, the Super Group 3 fax falls back in speed and operates at the speed of the Group 3 machine.
When V.34 fax machines initially contact each other, they use the V.8 protocol. According to the V.8 protocol, the answering fax machine (hereinafter sometime referred to as the called fax machine or as the second fax machine) generates a AnsAm tone (that is, a 2100 Hz tone with a 15 Hz envelope). The AnsAm tone tells the first fax machine that the second fax machine is V.8 capable. In response to the AnsAm tone, the first fax machine generates a Call Menu (CM) tone. The CM tone includes a set of all the fax modulations supported by the first fax machine. When the second fax machine receives the CM tone, it replies with a Joint Menu (JM) signal that indicates the particular modulation selected for that particular call, that is, the highest speed at which both machines can operate.
Fax machines connected over packet networks are generally connected using a protocol known as the T.38 protocol that includes a fax relay protocol. In May 2003, the T.38 fax relay protocol was extended to support the V.34 speed of 33,600 bps, that is the speed used by Super group 3 fax machines. However, many of the T.38 gateways that are presently deployed have not been upgraded to handle the V.34, 33,600 bps speed, in fax relay mode. Hereinafter, the following terms will be used with the following meanings:                1) Enhanced T.38 Protocol: The T.38 protocol which has been enhanced to handle V.34, 33,600 bps speed, in fax relay mode, will be referred to as the enhanced T.38 protocol.        2) Un-enhanced T.38 protocol: The T.38 protocol which has not been enhanced to handle V.34 speed, in fax relay mode, will be called the un-enhanced T.38 protocol.        3) Enhanced T.38 Gateway: A Gateway operating according to the enhanced T.38 protocol will be referred to as an enhanced T.38 Gateway.        4) Un-enhanced T.38 Gateway: A Gateway operating according to the un-enhanced T.38 protocol will be referred to as an un-enhanced T.38 Gateway.        
Prior co-pending application Ser. No. 10/743,980 filed Dec. 22, 2003 (c-316) describes a method and system for connecting V.34 enabled fax machines (that is fax machines capable of operating at 33,600 bps) over network gateways that use the un-enhanced T.38 protocol. With the method and system described in application Ser. No. 10/743,980, either the AnsAm signal or the CM signal is modified so that the fax machine falls back to a non V.34 protocol and operates at a slower speed which the un-enhanced T.38 gateway is capable of handling.
The above described technique functions if the fax machines involved conform to the appropriate standards; however, it has been found that some of the fax machines that are in widespread use do not function as specified by the various standards and with some of the fax machines in widespread use, the above described technique does not always operate satisfactorily.